318 to stock 340 power level questions.

to autox,
better head for a bigger motor, yes.
but I don't believe so at this level of 318.

I have a 318 in the shop that has .020 stock pistons, 318 closed chambered '234' truck heads, 340 crane blue print cam w/4* advance, and headers, eddy performer/600 eddy carb.
It runs hard to 6100rpm then turns off like a light switch, but it make great power and breaks tires shifting with a 4 spd, it's my back up motor.

the heads were un touched too.

just keep it simple bro and you'll be good.